Lithium ion batteries having layered type lithium cobalt oxide (LiCoO2) as cathode electrode and graphite type carbon as anode electrode are widely used in portable electronic devices and are developing for electric vehicle market. LiCoO2 has high capacity, high voltage, long cycling life, and stable electrochemical performance, but scarce cobalt is expensive. In addition, the decomposing of LiCoO2 by heat generated at the discharge state obstructs the applications of lithium ion batteries. To achieve lower price, higher specific capacity, and safety, studies have been made in new types of cathode active materials.
Current research in cathode active material of lithium ion battery has shifted to ternary materials, such as LiNi1-x-yMnxCoyO2, which has the same layered structure as LiCoO2. Particularly, LiNi1/3Co1/3Mn1/3O2 and LiNi0.4Mn0.4Co0.2O2 have similar electrochemical performance to LiCoO2. Compared to LiCoO2, LiNi1/3Co1/3Mn1/3O2 and LiNi0.4Mn0.4Co0.2O2 have lower cost, better thermal stability, and ease of synthesis. However, these two materials have relatively low specific capacity. To improve the specific capacity, increases in the content of Ni in the ternary materials are made, developing a series of high Ni cathode active materials, such as LiNi0.5Mn0.3Co0.2O2, LiNi0.66Co0.17Mn0.17O2, LiNi0.7Co0.15Mn0.15O2, and LiNi0.8Co0.1Mn0.1O2. LiNi0.8Co0.1Mn0.1O2 not only has a high specific capacity, but also has a good thermal stability.
However, LiNi0.8Co0.1Mn0.1O2 is still less than ideal in terms of specific capacity and capacity retention, and capacity loss after numerous cycles.